I have Linux Virtual machine (ubuntu 12.04) installed on my Mac OS.
On my terminal,
email@example.com:~$ su password: su : Authentication failure firstname.lastname@example.org:~$ ls -lth /bin/su -rwsr-sr-x 1 root root 36K Sep 12 2012 /bin/su
But the following works:
email@example.com:~$ sudo ls [sudo] password for user: (....lists the directories) firstname.lastname@example.org:~$ sudo -s [sudo] password for user: email@example.com:~#
Hence the question is,
sudo -s works and logs in as root, while
su results in authentication failure.
I typed the passwords correctly each time.
sudo ls works